1. Field of the Invention
This invention relates to flame retardant silicone elastomers.
2. Description of the Prior Art
Curable silicone elastomers comprising vinyl-containing polydiorganosiloxane fluids and organohydrogensiloxane fluids containing silicon-bonded hydrogen atoms cured through the use of a platinum catalyst are well known in the art. Compositions containing platinum compounds to improve the flame resistance are disclosed in Canadian Pat. No. 768,223 to Compton. Such materials have a certain amount of resistance to burning.
The use of platinum as a catalyst for the reaction of a compound containing a silicon-bonded hydrogen atom with a compound containing aliphatic unsaturation to establish a new Si--C bond is disclosed in U.S. Pat. No. 2,823,218. Many elastomeric products based on this reaction have become commercially available. An object of this invention is to improve the flame retardancy of elastomers cured using this method.
A polysiloxane composition curable to a fire resistant elastomer has been disclosed by Milbert in U.S. Pat. No. 3,821,140. The composition of Milbert comprises 100 parts of at least one diorganopolysiloxane rubber of viscosity 2 million to 80 million centipoises (2000-80,000 Pa.sup.. s) at 25.degree. C., 5 to 100 parts of at least one inorganic filler, 0.2 to 5 parts of an organic peroxide, 0.001 to 0.01 parts of platinum and either 3 to 35 parts in total of at least one rare earth metal oxide or 1 to 8 parts in total of at least one rare earth metal hydroxide. Milbert's compositions are cured by heating through the use of an organic peroxide by molding under pressure, followed by oven heating.
The compositions of the present invention are of such a viscosity that they may be formed into the desired shape by gravitational flow. The use of heavy molds or equipment to withstand high molding pressures is unnecessary. The use of expensive organic peroxides is not necessary in the present invention in order to effect a cure, whereas the ingredients of the present invention react in the presence of a platinum catalyst to produce the desired cure.
Ceric hydrate has been used commercially to improve the heat stability of organic peroxide cured silicone elastomers. Its use in vinyl-containing polymers with viscosities below 30 Pa.sup.. s to improve heat stability has been prevented by the tendency of such mixtures to exhibit poor shelf life. When such mixtures have been attempted the resulting compositions show a rise in viscosity to the point where they are no longer capable of being molded in the desired manner.